Secondary metabolites produced by fungi often find their way into food products consumed by man and his animals. In this respect, Fusarium roseum colonize cereal grains and during its invasion, produces zearalenone and trichothecene toxins. Zearalenone is an estrogen that affects man as well as animals and is often found in animal feeds. Trichothecenes cause hemorrhaging and predisposition to disease. Our greatest attention is focused on zearalenone and we have recently found that the cis isomer is 5 times more active than the naturally occurring trans isomer. Moreover, both isomers strongly bind to mammalian protein receptor molecules and displace estradiol competitively. These findings prompt us to test the chemotherapeutant activity of the zearalenones in breast cancer. Further, other derivatives are being synthesized to test their affinity for the protein receptor and remission of breast cancer. Additional experiments on the metabolism of these toxins in animal is being conducted in order to ascertain the magnitude of residue in edible animal tissue.